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URL dispatch provides a simple way to map URLs to view code
using a simple pattern matching language. An ordered set of patterns is
checked one by one. If one of the patterns matches the path information
associated with a request, a particular view callable is invoked. A
view callable is a specific bit of code, defined in your application, that
receives the request and returns a response object.

Route configuration is the act of adding a new route to an
application. A route has a name, which acts as an identifier to be used for
URL generation. The name also allows developers to associate a view
configuration with the route. A route also has a pattern, meant to match
against the PATH_INFO portion of a URL (the portion following the scheme
and port, e.g., /foo/bar in the URL http://localhost:8080/foo/bar). It
also optionally has a factory and a set of route predicate
attributes.

# "config" below is presumed to be an instance of the# pyramid.config.Configurator class; "myview" is assumed# to be a "view callable" functionfromviewsimportmyviewconfig.add_route('myroute','/prefix/{one}/{two}')config.add_view(myview,route_name='myroute')

When a view callable added to the configuration by way of
add_view() becomes associated with a route
via its route_name predicate, that view callable will always be found and
invoked when the associated route pattern matches during a request.

More commonly, you will not use any add_view statements in your project's
"setup" code. You will instead use add_route statements, and use a
scan to associate view callables with routes. For example, if this is
a portion of your project's __init__.py:

Note that we don't call add_view() in this
setup code. However, the above scan execution
config.scan('mypackage') will pick up each configuration
decoration, including any objects decorated with the
pyramid.view.view_config decorator in the mypackage Python
package. For example, if you have a views.py in your package, a scan will
pick up any of its configuration decorators, so we can add one there that
references myroute as a route_name parameter:

The syntax of the pattern matching language used by Pyramid URL dispatch
in the pattern argument is straightforward. It is close to that of the
Routes system used by Pylons.

The pattern used in route configuration may start with a slash character. If
the pattern does not start with a slash character, an implicit slash will be
prepended to it at matching time. For example, the following patterns are
equivalent:

{foo}/bar/baz

and:

/{foo}/bar/baz

If a pattern is a valid URL it won't be matched against an incoming request.
Instead it can be useful for generating external URLs. See External
routes for details.

A pattern segment (an individual item between / characters in the pattern)
may either be a literal string (e.g., foo) or it may be a replacement
marker (e.g., {foo}), or a certain combination of both. A replacement
marker does not need to be preceded by a / character.

A replacement marker is in the format {name}, where this means "accept any
characters up to the next slash character and use this as the namematchdict value."

A replacement marker in a pattern must begin with an uppercase or lowercase
ASCII letter or an underscore, and can be composed only of uppercase or
lowercase ASCII letters, underscores, and numbers. For example: a,
a_b, _b, and b9 are all valid replacement marker names, but 0a
is not.

Changed in version 1.2: A replacement marker could not start with an underscore until Pyramid 1.2.
Previous versions required that the replacement marker start with an
uppercase or lowercase letter.

A matchdict is the dictionary representing the dynamic parts extracted from a
URL based on the routing pattern. It is available as request.matchdict.
For example, the following pattern defines one literal segment (foo) and
two replacement markers (baz, and bar):

foo/{baz}/{bar}

The above pattern will match these URLs, generating the following matchdicts:

The match for a segment replacement marker in a segment will be done only up to
the first non-alphanumeric character in the segment in the pattern. So, for
instance, if this route pattern was used:

foo/{name}.html

The literal path /foo/biz.html will match the above route pattern, and the
match result will be {'name':u'biz'}. However, the literal path
/foo/biz will not match, because it does not contain a literal .html at
the end of the segment represented by {name}.html (it only contains
biz, not biz.html).

To capture both segments, two replacement markers can be used:

foo/{name}.{ext}

The literal path /foo/biz.html will match the above route pattern, and the
match result will be {'name':'biz','ext':'html'}. This occurs because
there is a literal part of . (period) between the two replacement markers
{name} and {ext}.

Replacement markers can optionally specify a regular expression which will be
used to decide whether a path segment should match the marker. To specify that
a replacement marker should match only a specific set of characters as defined
by a regular expression, you must use a slightly extended form of replacement
marker syntax. Within braces, the replacement marker name must be followed by
a colon, then directly thereafter, the regular expression. The default
regular expression associated with a replacement marker [^/]+ matches one
or more characters which are not a slash. For example, under the hood, the
replacement marker {foo} can more verbosely be spelled as {foo:[^/]+}.
You can change this to be an arbitrary regular expression to match an arbitrary
sequence of characters, such as {foo:\d+} to match only digits.

It is possible to use two replacement markers without any literal characters
between them, for instance /{foo}{bar}. However, this would be a
nonsensical pattern without specifying a custom regular expression to restrict
what each marker captures.

Segments must contain at least one character in order to match a segment
replacement marker. For example, for the URL /abc/:

/abc/{foo} will not match.

/{foo}/ will match.

Note that values representing matched path segments will be URL-unquoted and
decoded from UTF-8 into Unicode within the matchdict. So for instance, the
following pattern:

foo/{bar}

When matching the following URL:

http://example.com/foo/La%20Pe%C3%B1a

The matchdict will look like so (the value is URL-decoded / UTF-8 decoded):

{'bar':u'La Pe\xf1a'}

Literal strings in the path segment should represent the decoded value of the
PATH_INFO provided to Pyramid. You don't want to use a URL-encoded value
or a bytestring representing the literal encoded as UTF-8 in the pattern. For
example, rather than this:

/Foo%20Bar/{baz}

You'll want to use something like this:

/Foo Bar/{baz}

For patterns that contain "high-order" characters in its literals, you'll want
to use a Unicode value as the pattern as opposed to any URL-encoded or
UTF-8-encoded value. For example, you might be tempted to use a bytestring
pattern like this:

/La Pe\xc3\xb1a/{x}

But this will either cause an error at startup time or it won't match properly.
You'll want to use a Unicode value as the pattern instead rather than raw
bytestring escapes. You can use a high-order Unicode value as the pattern by
using Python source file encoding plus the "real" character in the
Unicode pattern in the source, like so:

/La Peña/{x}

Or you can ignore source file encoding and use equivalent Unicode escape
characters in the pattern.

/La Pe\xf1a/{x}

Dynamic segment names cannot contain high-order characters, so this applies
only to literals in the pattern.

If the pattern has a * in it, the name which follows it is considered a
"remainder match". A remainder match must come at the end of the pattern.
Unlike segment replacement markers, it does not need to be preceded by a slash.
For example:

foo/{baz}/{bar}*fizzle

The above pattern will match these URLs, generating the following matchdicts:

Note that when a *stararg remainder match is matched, the value put into
the matchdict is turned into a tuple of path segments representing the
remainder of the path. These path segments are URL-unquoted and decoded from
UTF-8 into Unicode. For example, for the following pattern:

foo/*fizzle

When matching the following path:

/foo/La%20Pe%C3%B1a/a/b/c

Will generate the following matchdict:

{'fizzle':(u'La Pe\xf1a', u'a', u'b', u'c')}

By default, the *stararg will parse the remainder sections into a tuple
split by segment. Changing the regular expression used to match a marker can
also capture the remainder of the URL, for example:

foo/{baz}/{bar}{fizzle:.*}

The above pattern will match these URLs, generating the following matchdicts:

This occurs because the default regular expression for a marker is [^/]+
which will match everything up to the first /, while {fizzle:.*} will
result in a regular expression match of .* capturing the remainder into a
single value.

Route configuration declarations are evaluated in a specific order when a
request enters the system. As a result, the order of route configuration
declarations is very important. The order in which route declarations are
evaluated is the order in which they are added to the application at startup
time. (This is unlike a different way of mapping URLs to code that
Pyramid provides, named traversal, which does not depend on
pattern ordering).

For routes added via the add_route method,
the order that routes are evaluated is the order in which they are added to the
configuration imperatively.

For example, route configuration statements with the following patterns might
be added in the following order:

members/{def}
members/abc

In such a configuration, the members/abc pattern would never be matched.
This is because the match ordering will always match members/{def} first;
the route configuration with members/abc will never be evaluated.

Many of these arguments are route predicate arguments. A route
predicate argument specifies that some aspect of the request must be true for
the associated route to be considered a match during the route matching
process. Examples of route predicate arguments are pattern, xhr, and
request_method.

Other arguments are name and factory. These arguments represent
neither predicates nor view configuration information.

The main purpose of route configuration is to match (or not match) the
PATH_INFO present in the WSGI environment provided during a request
against a URL path pattern. PATH_INFO represents the path portion of the
URL that was requested.

The way that Pyramid does this is very simple. When a request enters
the system, for each route configuration declaration present in the system,
Pyramid checks the request's PATH_INFO against the pattern
declared. This checking happens in the order that the routes were declared
via pyramid.config.Configurator.add_route().

When a route configuration is declared, it may contain route predicate
arguments. All route predicates associated with a route declaration must be
True for the route configuration to be used for a given request during a
check. If any predicate in the set of route predicate arguments
provided to a route configuration returns False during a check, that route
is skipped and route matching continues through the ordered set of routes.

If any route matches, the route matching process stops and the view
lookup subsystem takes over to find the most reasonable view callable for the
matched route. Most often, there's only one view that will match (a view
configured with a route_name argument matching the matched route). To gain
a better understanding of how routes and views are associated in a real
application, you can use the pviews command, as documented in
Displaying Matching Views for a Given URL.

When the URL pattern associated with a particular route configuration is
matched by a request, a dictionary named matchdict is added as an attribute
of the request object. Thus, request.matchdict will contain the
values that match replacement patterns in the pattern element. The keys in
a matchdict will be strings. The values will be Unicode objects.

Note

If no route URL pattern matches, the matchdict object attached to the
request will be None.

When the URL pattern associated with a particular route configuration is
matched by a request, an object named matched_route is added as an
attribute of the request object. Thus, request.matched_route will
be an object implementing the IRoute interface
which matched the request. The most useful attribute of the route object is
name, which is the name of the route that matched.

Note

If no route URL pattern matches, the matched_route object attached to
the request will be None.

The simplest route declaration which configures a route match to directly
result in a particular view callable being invoked:

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2

config.add_route('idea','site/{id}')config.scan()

When a route configuration with a view attribute is added to the system,
and an incoming request matches the pattern of the route configuration, the
view callable named as the view attribute of the route
configuration will be invoked.

Recall that the @view_config is equivalent to calling config.add_view,
because the config.scan() call will import mypackage.views, shown
below, and execute config.add_view under the hood. Each view then maps the
route name to the matching view callable. In the case of the above example,
when the URL of a request matches /site/{id}, the view callable at the
Python dotted path name mypackage.views.site_view will be called with the
request. In other words, we've associated a view callable directly with a
route pattern.

When the /site/{id} route pattern matches during a request, the
site_view view callable is invoked with that request as its sole argument.
When this route matches, a matchdict will be generated and attached to the
request as request.matchdict. If the specific URL matched is /site/1,
the matchdict will be a dictionary with a single key, id; the value
will be the string '1', ex.: {'id':'1'}.

The above configuration will allow Pyramid to service URLs in these
forms:

/ideas/{idea}
/users/{user}
/tags/{tag}

When a URL matches the pattern /ideas/{idea}, the view callable
available at the dotted Python pathname mypackage.views.idea_view will
be called. For the specific URL /ideas/1, the matchdict generated
and attached to the request will consist of {'idea':'1'}.

When a URL matches the pattern /users/{user}, the view callable
available at the dotted Python pathname mypackage.views.user_view will be
called. For the specific URL /users/1, the matchdict generated and
attached to the request will consist of {'user':'1'}.

When a URL matches the pattern /tags/{tag}, the view callable available
at the dotted Python pathname mypackage.views.tag_view will be called.
For the specific URL /tags/1, the matchdict generated and attached to
the request will consist of {'tag':'1'}.

In this example we've again associated each of our routes with a view
callable directly. In all cases, the request, which will have a matchdict
attribute detailing the information found in the URL by the process will be
passed to the view callable.

The context resource object passed in to a view found as the result of
URL dispatch will, by default, be an instance of the object returned by the
root factory configured at startup time (the root_factory argument
to the Configurator used to configure the application).

You can override this behavior by passing in a factory argument to the
add_route() method for a particular route.
The factory should be a callable that accepts a request and returns
an instance of a class that will be the context resource used by the view.

Here, request.context is an instance of Idea. If indeed the resource
object is a SQLAlchemy model, you do not even have to perform a query in the
view callable, since you have access to the resource via request.context.

Use the pyramid.request.Request.route_url() method to generate URLs based
on route patterns. For example, if you've configured a route with the name
"foo" and the pattern "{a}/{b}/{c}", you might do this.

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url=request.route_url('foo',a='1',b='2',c='3')

This would return something like the string http://example.com/1/2/3 (at
least if the current protocol and hostname implied http://example.com).

Replacement values passed to route_url or route_path must be Unicode or
bytestrings encoded in UTF-8. One exception to this rule exists: if you're
trying to replace a "remainder" match value (a *stararg replacement value),
the value may be a tuple containing Unicode strings or UTF-8 strings.

Note that URLs and paths generated by route_url and route_path are
always URL-quoted string types (they contain no non-ASCII characters).
Therefore, if you've added a route like so:

config.add_route('la',u'/La Peña/{city}')

And you later generate a URL using route_path or route_url like so:

url=request.route_path('la',city=u'Québec')

You will wind up with the path encoded to UTF-8 and URL-quoted like so:

/La%20Pe%C3%B1a/Qu%C3%A9bec

If you have a *stararg remainder dynamic part of your route pattern:

config.add_route('abc','a/b/c/*foo')

And you later generate a URL using route_path or route_url using a
string as the replacement value:

url=request.route_path('abc',foo=u'Québec/biz')

The value you pass will be URL-quoted except for embedded slashes in the
result:

/a/b/c/Qu%C3%A9bec/biz

You can get a similar result by passing a tuple composed of path elements:

url=request.route_path('abc',foo=(u'Québec',u'biz'))

Each value in the tuple will be URL-quoted and joined by slashes in this case:

Routes added with a Truestatic keyword argument will never be
considered for matching at request time. Static routes are useful for URL
generation purposes only. As a result, it is usually nonsensical to provide
other non-name and non-pattern arguments to
add_route() when static is passed as
True, as none of the other arguments will ever be employed. A single
exception to this rule is use of the pregenerator argument, which is not
ignored when static is True.

Adding append_slash=True is a way to automatically redirect requests where
the URL lacks a trailing slash, but requires one to match the proper route.
When configured, along with at least one other route in your application, this
view will be invoked if the value of PATH_INFO does not already end in a
slash, and if the value of PATH_INFOplus a slash matches any route's
pattern. In this case it does an HTTP redirect to the slash-appended
PATH_INFO. In addition you may pass anything that implements
pyramid.interfaces.IResponse which will then be used in place of the
default class (pyramid.httpexceptions.HTTPFound).

Let's use an example. If the following routes are configured in your
application:

If a request enters the application with the PATH_INFO value of
/no_slash, the first route will match and the browser will show "No slash".
However, if a request enters the application with the PATH_INFO value of
/no_slash/, no route will match, and the slash-appending not found view
will not find a matching route with an appended slash. As a result, the
notfound view will be called and it will return a "Not found" body.

If a request enters the application with the PATH_INFO value of
/has_slash/, the second route will match. If a request enters the
application with the PATH_INFO value of /has_slash, a route will be
found by the slash-appending Not Found View. An HTTP redirect to
/has_slash/ will be returned to the user's browser. As a result, the
notfound view will never actually be called.

It's useful to be able to take a peek under the hood when requests that enter
your application aren't matching your routes as you expect them to. To debug
route matching, use the PYRAMID_DEBUG_ROUTEMATCH environment variable or
the pyramid.debug_routematch configuration file setting (set either to
true). Details of the route matching decision for a particular request to
the Pyramid application will be printed to the stderr of the console
which you started the application from. For example:

The pyramid.config.Configurator.include() method accepts an argument
named route_prefix which can be useful to authors of URL-dispatch-based
applications. If route_prefix is supplied to the include method, it must
be a string. This string represents a route prefix that will be prepended to
all route patterns added by the included configuration. Any calls to
pyramid.config.Configurator.add_route() within the included callable will
have their pattern prefixed with the value of route_prefix. This can be
used to help mount a set of routes at a different location than the included
callable's author intended while still maintaining the same route names. For
example:

In the above configuration, the show_users route will have an effective
route pattern of /users/show instead of /show because the
route_prefix argument will be prepended to the pattern. The route will
then only match if the URL path is /users/show, and when the
pyramid.request.Request.route_url() function is called with the route
name show_users, it will generate a URL with that same path.

Route prefixes are recursive, so if a callable executed via an include itself
turns around and includes another callable, the second-level route prefix will
be prepended with the first:

In the above configuration, the show_users route will still have an
effective route pattern of /users/show. The show_times route, however,
will have an effective pattern of /users/timing/times.

Route prefixes have no impact on the requirement that the set of route names
in any given Pyramid configuration must be entirely unique. If you compose
your URL dispatch application out of many small subapplications using
pyramid.config.Configurator.include(), it's wise to use a dotted name for
your route names so they'll be unlikely to conflict with other packages that
may be added in the future. For example:

Each of the predicate callables fed to the custom_predicates argument of
add_route() must be a callable accepting two
arguments. The first argument passed to a custom predicate is a dictionary
conventionally named info. The second argument is the current
request object.

The info dictionary has a number of contained values, including match
and route. match is a dictionary which represents the arguments matched
in the URL by the route. route is an object representing the route which
was matched (see pyramid.interfaces.IRoute for the API of such a route
object).

info['match'] is useful when predicates need access to the route match.
For example:

The above any_of function generates a predicate which ensures that the
match value named segment_name is in the set of allowable values
represented by allowed. We use this any_of function to generate a
predicate function named num_one_two_or_three, which ensures that the
num segment is one of the values one, two, or three , and use
the result as a custom predicate by feeding it inside a tuple to the
custom_predicates argument to
add_route().

A custom route predicate may also modify the match dictionary. For
instance, a predicate might do some type conversion of values:

Now the try/except is no longer needed because the route will not match at all
unless these markers match \d+ which requires them to be valid digits for
an int type conversion.

The match dictionary passed within info to each predicate attached to a
route will be the same dictionary. Therefore, when registering a custom
predicate which modifies the match dict, the code registering the predicate
should usually arrange for the predicate to be the last custom predicate in
the custom predicate list. Otherwise, custom predicates which fire subsequent
to the predicate which performs the match modification will receive the
modified match dictionary.

Warning

It is a poor idea to rely on ordering of custom predicates to build a
conversion pipeline, where one predicate depends on the side effect of
another. For instance, it's a poor idea to register two custom predicates,
one which handles conversion of a value to an int, the next which handles
conversion of that integer to some custom object. Just do all that in a
single custom predicate.

The route object in the info dict is an object that has two useful
attributes: name and pattern. The name attribute is the route name.
The pattern attribute is the route pattern. Here's an example of using the
route in a set of route predicates:

Although it is not a particularly common need in basic applications, a "route"
configuration declaration can mention a "factory". When a route matches a
request, and a factory is attached to the route, the root factory
passed at startup time to the Configurator is ignored. Instead the
factory associated with the route is used to generate a root object.
This object will usually be used as the context resource of the view
callable ultimately found via view lookup.

Pyramid provides its own security framework which consults an
authorization policy before allowing any application code to be called.
This framework operates in terms of an access control list, which is stored as
an __acl__ attribute of a resource object. A common thing to want to do is
to attach an __acl__ to the resource object dynamically for declarative
security purposes. You can use the factory argument that points at a
factory which attaches a custom __acl__ to an object at its creation time.

If the route archives/{article} is matched, and the article number is
1, Pyramid will generate an Articlecontext resource
with an ACL on it that allows the editor principal the view permission.
Obviously you can do more generic things than inspect the route's match dict to
see if the article argument matches a particular string. Our sample
Article factory class is not very ambitious.

When a request enters the system which matches the pattern of the route, the
usual result is simple: the view callable associated with the route is
invoked with the request that caused the invocation.

For most usage, you needn't understand more than this. How it works is an
implementation detail. In the interest of completeness, however, we'll explain
how it does work in this section. You can skip it if you're uninterested.

When a view is associated with a route configuration, Pyramid ensures
that a view configuration is registered that will always be found
when the route pattern is matched during a request. To do so:

A special route-specific interface is created at startup time for
each route configuration declaration.

When an add_view statement mentions a routename attribute, a
view configuration is registered at startup time. This view
configuration uses a route-specific interface as a request type.

At runtime, when a request causes any route to match, the request
object is decorated with the route-specific interface.

The fact that the request is decorated with a route-specific interface causes
the view lookup machinery to always use the view callable registered
using that interface by the route configuration to service requests that
match the route pattern.

As we can see from the above description, technically, URL dispatch doesn't
actually map a URL pattern directly to a view callable. Instead URL dispatch
is a resource location mechanism. A Pyramidresource
location subsystem (i.e., URL dispatch or traversal) finds a
resource object that is the context of a request. Once
the context is determined, a separate subsystem named view
lookup is then responsible for finding and invoking a view callable
based on information available in the context and the request. When URL
dispatch is used, the resource location and view lookup subsystems provided by
Pyramid are still being utilized, but in a way which does not require a
developer to understand either of them in detail.